The present invention relates to an electrical contact pin for mounting in a plated-through hole in a printed circuit board. More particularly, this invention relates to a contact pin which has a contact section which interacts with the hole and the metallization therein. The cross-section of the contact section is in the shape of an H and has four projecting bendable fins along the legs of the H which extend over the longitudinal distance of the contact section and thereby define two longitudinal recesses situated on both sides of the crossbar. A contact pin of this type is described in U.S. Pat. No. 3,827,004 granted July 30, 1984 and assigned to the same assignee as the present application.
In the case of the contact pin disclosed in U.S. Pat. No. 3,827,004, the four fins are gradually bent inwards when the pin is introduced into the hole in the printed circuit board so that the contact section is fixed at four points in the hole. The H-shaped construction reduces or eliminates the risk of rotating the pin during mounting. As a result, square pins of the type used on a large scale in the printed circuit board industry can then be used. The pairs of fins situated on both sides of the transverse section of the H-shaped contact section project perpendicularly from the said transverse section of the pin. In the introduction and final fixing of the contact section of the pin in the respective hole it is of the greatest importance that the projecting fins are constructed absolutely symmetrically and have the same thickness so that during the insertion movement into the hole all four are bent uniformly and grip the metallization in the hole. Even with very small differences in the thickness, and consequently in the stiffness, of the projecting fins, a different force acting on each fin will consequently occur on introducing the contact section into the hole. Rotation or eccentric positioning of the pin will result. This may cause serious damage to the metallization in the hole and even positioning of the pin becomes very difficult.
In practice these pins are almost always made from square wire or flat tape material, the recesses of the contact section being formed by stamping technology and the fins being forced outwards or extruded.
As a result of the flat floor on either side of the crossbar of the H-shaped contact section and the dies used for this purpose, the recesses are not completely centered and symmetrically formed in the stamping operation. As a result of the "floating" of the stamping operation, a truly absolute centering of the resultant recess is not obtained. Consequently, the fins obtained on both sides of the recess are virtually never of truly equal thickness or height. On introducing a contact section of this type into the hole of the printed circuit board, an unequal distribution of force occurs and one fin will bend earlier as a result of the lesser thickness, which in turn may cause the pin to rotate. This may damage the metallization more than is minimally acceptable and even positioning of the pin may become impossible.
A further problem is that, due to the sharp angles which the fins make with the flat floor of the crossbar section of the H-shaped contact section. bending and or even cracking easily occurs in these angles during the insertion movement.
A different version of such a H-shaped pin is described in U.S. Pat. No. 4,469,394 granted Sept. 4, 1984, and also assigned to the same assignee as the present invention. The contact pin described in the patent has a serrated floor in order to better control the height of the fins. The extension which occurs during the deformations was found to be a disadvantage. It was possible to solve this partially by using this serrated floor, but not as yet with the desired result in relation to the desired symmetry.